How to Debitter Olive Oil for Emulsions

Olive oil being poured into small dish

[Photograph: J. Kenji López-Alt]

Editors’ Note: Nik Sharma’s new book, The The Flavor Equation: The Science of Great Cooking Explained in More Than 100 Essential Recipes, comes out in October 2020. You can pre-order it anywhere books are sold.

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There are two kinds of people in this world: Those who love mayonnaise, and everyone else.

I’m a member of the first group. I like to eat French fries with a little bit of mayo on the side and, in summer, when tomatoes are at their peak, you can’t keep me away from juicy tomato slices piled high on white bread painted liberally with mayonnaise. So it’s not surprising that I’ve tried to squeeze a mayonnaise recipe into both of my cookbooks.

For my first cookbook, Season: Big Flavors, Beautiful Food, I worked on a mayonnaise that used olive oil as an ingredient, but I ran into a problem—a lingering, unpleasantly bitter aftertaste. At the time, I couldn’t figure out a way to get rid of the bitterness, so I dropped the recipe. When I started to work on my second book, The Flavor Equation, it only felt right to revisit the bitterness problem and figure out a way to fix it; after all, this book is about the science of flavor.

Bitterness is one of the five basic tastes currently accepted by science (sour, sweet, salty, and umami or savory are the others, although other tastes, like the taste of fat, or oleogustus, are currently under research). Our ability to taste bitter foods evolved as a protective mechanism to help us avoid ingesting toxic and harmful substances. However, not all bitter substances are dangerous to us; in fact, some foods, like cocoa, tea, collards, and bitter melon contain bitter-tasting substances called phytonutrients. Genetics are also responsible for making some of us much more sensitive to bitterness in foods through variations in the sequence of our DNA. I, for one, have avoided bitter foods like bitter melon at all costs, no matter how many times my parents tried to convince me to eat it. (They eventually gave up.)

While olive oil by itself isn’t bitter to taste, when present in emulsions like mayonnaise and aioli it can make them taste bitter. When developing the recipe for the mayonnaise in my cookbook, I also attempted to use mustard oil as an alternate option, but that, too, yielded a very bitter-tasting mayonnaise, which led me to conclude there was some quality these two oils shared that produced the same effect.

Bottle of Yandilla mustard oil

A bottle of mustard oil. [Photograph: Vicky Wasik]

The most obvious question to ask is: Where is the bitter taste coming from? One possibility is the presence of free fatty acids in olive oil, which, depending on the type of fatty acid, can taste bitter and even pungent. Depending on the variety of olives used and how the oil was extracted, one can expect different levels of these free fatty acids in oil. However, a more promising explanation for the bitterness is the presence of polyphenols, like oleuropein in olive oil, which are known to taste bitter and scientists consider them to be responsible for the bitterness that shows up in olive-oil based mayonnaise. These polyphenols are also considered to be beneficial to our health but, as you will soon see, when it comes to mayonnaise, most of us steer away from products that contain them due to their bitter taste.

What are the possible solutions to avoid bitterness when making mayonnaise with olive oil? I asked a few chefs and home cooks what they do, and the most common answer was to avoid using olive oil completely or use a blend of olive oil and some other neutral-tasting oil like grapeseed or canola, or use a less flavorful kind of olive oil. I also considered trying to mask the bitterness by adding a lot of ingredients to the emulsion, but that didn’t work, as an emulsion can only accommodate so many different ingredients before it starts to fall apart and lose its luxurious structure, and the maximum capacity is insufficient to mask the bitterness entirely. Anyway, I wanted to make a mayonnaise that still had the full flavor of olive or mustard oil without the bitterness and without extraneous flavors.

As I started to try to figure out if it was possible, there were some clues that hinted at a possible solution:

  • First, since olive oil isn’t particularly bitter on its own, but will produce a bitter mayonnaise, this implies that polyphenols like oleuropein present in olive oil might also be soluble in water. One of the key criteria for a substance to act as a tastant, as defined by scientists, is that the substance should dissolve in water and interact with our taste receptors.
  • Another clue came from the way in which raw olive fruit are processed before they can be converted into table olives: The fruit are usually brined or pretreated with lye and then subjected to a variety of treatments, which help draw out or alter the oleuropein and other bitter polyphenols, and most of these are washed away.
  • Since mustard oil is also rich in polyphenols, if I could develop a method that worked for olive oil, it might apply to mustard oil, too.

Based on these observations, it occurred to me that by using some kind of solvent I might be able to extract the polyphenols out of the oil. I then looked up to see if any research had been performed on polyphenols in olive oil and their solubility. I tried a few different things, like using clear vodka—alcohol is often a wonderful solvent for extracting substances from oil (and other non-polar liquids)—but in my experiments at home, the mayonnaise made from alcohol-treated olive oil still tasted bitter. I mixed clear vodka at different temperatures with the olive and mustard oil, separately, and then used the oils to make mayonnaise, but no matter what I did, the mayo remained bitter.

As often is the case, the solution turned out to be much more simple and practical. While researching the chapter on bitterness of The Flavor Equation and hunting for a possible solution to my mayonnaise issue, I came across a research study that was looking at a way to extract and recover oleuropein and other phenolic compounds from olive leaf waste. The scientists determined that adding boiling water to the olive leaves yielded the maximum amount of polyphenols extracted. This is something I could easily do in my kitchen! This method also reminded me of making marmalade from citrus fruits—some recipes will call for the fruit to be boiled in water (which is then discarded) before they are cooked in sugar to help eliminate the bitter substances present.

What if I mixed olive oil with boiling hot water, would that do the trick? This method also had an extra advantage—there was no emulsifying agent like proteins or lecithin from the egg to hold the oil and water together. The simple emulsion of oil and water would eventually fall apart if left undisturbed, and I would be able to easily separate the oil from the water phase as it would float above the water.

Roasted potatoes on a plate with a small ramekin of curry leaf mustard oil mayonnaise

Roasted potatoes served with curry leaf mayonnaise made with debittered mustard oil. [Photograph: Nik Sharma]

I set out a few different samples of olive oil from different sources on my kitchen counter. One set of samples were treated with boiling water, another set with cold tap water, and one set of samples was left untreated to serve as a control. I sealed the jars and then shook them and let them sit for about 30 minutes to an hour, until the emulsion fell apart and the oil and water returned to their original positions in the bottle. I then collected the oil and used it to make mayonnaise.

The samples that were treated with boiling water produced mayonnaise that was free from any bitter taste, but it still carried the delicious taste of olive oil. I then repeated the same set of experiments using mustard oil and the results were reproducible—the water carried the bitter-tasting polyphenols away. I finally had a method to make olive oil- and mustard oil-based emulsions like mayonnaise and aioli that lacked the bitter taste but still carried their unique flavors.

There is a valid counter argument to be made for keeping polyphenols in oils like olive or mustard; after all, they are beneficial for health. However, since most of us either avoid using these oils when making emulsions or use blends, and there is only so much “bitter-taste masking” that can be achieved by adding different ingredients to mayonnaise before it starts to fall apart, I recommend this method. After all, you’re only going to use this debittered oil to make an emulsion like mayonnaise or aioli; use the regular untreated stuff for the rest of your daily cooking.

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